- A
Transport layer (Layer 4)
The Transport layer ensures end-to-end reliable data delivery (e.g., TCP) and segments data into segments (PDU name: segment).
- B
Data Link layer (Layer 2)
Why wrong: The Data Link layer handles node-to-node delivery and frames data, but not end-to-end delivery or segmentation.
- C
Network layer (Layer 3)
Why wrong: The Network layer handles logical addressing and routing (packets), but does not provide reliable end-to-end delivery or segment data; that is the Transport layer's job.
- D
Session layer (Layer 5)
Why wrong: The Session layer manages sessions (establish, maintain, terminate) but does not segment data or ensure reliable delivery.
- E
Transport layer (Layer 4) and Network layer (Layer 3)
Both layers are directly responsible: Transport for end-to-end reliable delivery and segmentation, Network for logical addressing and routing of packets. However, note that segmentation is exclusively a Transport layer function; Network layer does not segment.
Quick Answer
The answer is the Transport layer (Layer 4), which is the only OSI layer responsible for both end‑to‑end reliable delivery and segmenting data into smaller units. This is because protocols like TCP at Layer 4 provide acknowledgements, sequencing, and retransmissions to guarantee reliable data transfer, while simultaneously breaking large application data streams into manageable segments for transmission across the network. On the CCNA 200-301 v2 exam, this concept often appears in questions that test your ability to distinguish Layer 4 functions from those of the Network layer (Layer 3), which handles routing and packet forwarding but does not ensure delivery, or the Data Link layer (Layer 2), which only manages hop‑by‑hop framing. A common trap is confusing segmentation with packetization—remember that segmentation is strictly a Layer 4 job, while fragmentation occurs at Layer 3. To lock this in, use the mnemonic: “TCP Takes Care of Transport and Trimming,” where “Trimming” reminds you of segmentation and “Takes Care” of reliable delivery.
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which single OSI model layer is responsible for both end‑to‑end reliable data delivery and segmenting data into smaller units?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Transport layer (Layer 4)
The Transport layer (Layer 4) is the only layer that ensures end‑to‑end reliable delivery using protocols like TCP that provide acknowledgements, sequencing, and retransmissions. At the same time, it segments large application data streams into smaller segments suitable for transmission. The Data Link layer (Layer 2) handles hop‑by‑hop framing but not end‑to‑end reliability. The Network layer (Layer 3) routes packets but does not guarantee delivery. The Session layer (Layer 5) manages sessions, not reliability or segmentation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Transport layer (Layer 4)
Why this is correct
The Transport layer ensures end-to-end reliable data delivery (e.g., TCP) and segments data into segments (PDU name: segment).
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Data Link layer (Layer 2)
Why it's wrong here
The Data Link layer handles node-to-node delivery and frames data, but not end-to-end delivery or segmentation.
- ✗
Network layer (Layer 3)
Why it's wrong here
The Network layer handles logical addressing and routing (packets), but does not provide reliable end-to-end delivery or segment data; that is the Transport layer's job.
- ✗
Session layer (Layer 5)
Why it's wrong here
The Session layer manages sessions (establish, maintain, terminate) but does not segment data or ensure reliable delivery.
- ✓
Transport layer (Layer 4) and Network layer (Layer 3)
Why this is correct
Both layers are directly responsible: Transport for end-to-end reliable delivery and segmentation, Network for logical addressing and routing of packets. However, note that segmentation is exclusively a Transport layer function; Network layer does not segment.
Related concept
Read the scenario before looking for a memorised answer.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Transport layer (Layer 4)Correct answer▾
Why this is correct
The Transport layer ensures end-to-end reliable data delivery (e.g., TCP) and segments data into segments (PDU name: segment).
✗Data Link layer (Layer 2)Wrong answer — click to see why▾
Why this is wrong here
The Data Link layer (Layer 2) handles node-to-node delivery within the same network segment, not end-to-end across multiple networks. It frames data into frames and adds physical addressing (MAC addresses), but does not segment data from upper layers or provide reliable end-to-end delivery.
Why candidates choose this
Students might confuse the Data Link layer's framing with segmentation, as both involve breaking data into smaller units. However, framing occurs at Layer 2 and is for local delivery, while segmentation at Layer 4 is for end-to-end transport.
✗Network layer (Layer 3)Wrong answer — click to see why▾
Why this is wrong here
The Network layer (Layer 3) is responsible for logical addressing (IP addresses) and routing packets across networks, but it does not provide reliable end-to-end delivery or segment data. Reliable delivery and segmentation are functions of the Transport layer.
Why candidates choose this
Students might think the Network layer handles segmentation because it deals with packets, but packets are the PDU of Layer 3 and are created from segments. The actual segmentation occurs at Layer 4.
✗Session layer (Layer 5)Wrong answer — click to see why▾
Why this is wrong here
The Session layer (Layer 5) manages sessions, including establishing, maintaining, and terminating connections between applications. It does not segment data or ensure reliable delivery; those are Transport layer functions.
Why candidates choose this
Students might associate 'session' with end-to-end communication and mistakenly think the Session layer handles reliable delivery. However, reliability is a Transport layer responsibility.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many learners mistakenly pick the Network layer (Layer 3) because they associate it with IP and packet delivery; however, IP is connectionless and unreliable, while end‑to‑end reliable delivery is exclusively a function of the Transport layer.
Detailed technical explanation
How to think about this question
TCP at Layer 4 uses a sliding window mechanism to manage flow control and ensure reliable delivery by tracking which segments have been acknowledged; if a segment is lost, TCP retransmits it based on timers or duplicate ACKs. Segmentation at Layer 4 involves breaking application data into segments with a TCP header (20-60 bytes) that includes source and destination ports, sequence numbers, and checksums, which are then passed to Layer 3 for packetization. In contrast, Layer 2 frames are limited to a single hop and do not provide end-to-end reliability, as they rely on Layer 4 for that function.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Network Infrastructure and Connectivity — study guide chapter
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Transport layer (Layer 4) — The Transport layer (Layer 4) is the only layer that ensures end‑to‑end reliable delivery using protocols like TCP that provide acknowledgements, sequencing, and retransmissions. At the same time, it segments large application data streams into smaller segments suitable for transmission. The Data Link layer (Layer 2) handles hop‑by‑hop framing but not end‑to‑end reliability. The Network layer (Layer 3) routes packets but does not guarantee delivery. The Session layer (Layer 5) manages sessions, not reliability or segmentation.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 11, 2026
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.
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